Internal combustion engines heretofore have provisions for exhausting gases through an exhaust system for noise and pollution control. It has been found that under certain conditions the passageways in the exhaust system become restrictive resulting in the restriction of the volumetric flow of exhaust gases, creating a higher than normal backpressure in the exhaust system effecting the performance of the engine. The construction of the exhaust systems heretofore normally are not provided with means to measure the amount of pressures creating the backpressure in the exhaust system, therefore it is difficult to diagnose a restrictive exhaust system having a higher than normal backpressure.